The aromatic aldehydes represented by the above general formula (IX) are used as perfumes (for example, heliotropin, veratraldehyde, etc.), or are important intermediates for medicines, agricultural chemicals, etc.
An object of the present invention is to provide a process for preparing such aromatic aldehydes inexpensively with industrial advantages.
As the conventional process for preparing the aromatic aldehydes represented by the general formula (IX), for example, heliotropin (piperonal), there is known a process of isomerizing and oxidizing in which safrole contained in the essential oil of Octoea Cymbarum is used as the starting material (disclosed in U.S. Pat. No. 2,916,499). However, this process has the defect that the supplied amount and the price of the starting material are unstable due to its dependence upon the natural world and involves problems about safety of safrole or isosafrole. Thus, processes using synthetic chemicals as starting materials have been demanded.
As one of such processes, there is known a process of using, as a starting material, methylenedioxybenzene which is prepared from pyrocatechol. This methylenedioxybenzene is directly formylated [process (1): Japanese patent application (OPI) No. 156867/77 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application")], chloromethylated [process (2): J. Gen. Chem., 8, 975 (1938) and British Pat. No. 1,538,214], or converted to a mandelic acid type compound [process (3): Belgian Pat. No. 877,911, German Pat. No. 2,754,490 and Current Sci., (India) 27, 22 (1958)].
However, process (1) has the defects that N-methylformanilide is not inexpensive, that N-methylaniline formed as a by-product from N-methylformanilide is recovered only in low yield, and that formic acid must be used for preparing N-methylformanilide from N-methylaniline, thus being unsatisfactory as an industrial process. Further, 50 to 60% of 1,2-methylenedioxybenzene is recovered in an unreacted state, and hence an energy loss is so serious that it is disadvantageous as an industrial process.
Process (2) has such defects as that it provides the end product in a yield as low as 55 to 60% based on methylenedioxybenzene, that a large amount of a tar-like material is formed as a by-product, that it requires complicated reaction procedures, and that a metal hydroxide formed as a by-product must be properly treated.
Process (3) has such defects as that glyoxalic acid used as one of the starting materials is expensive, that it requires to use a heavy metal like a copper catalyst in the step of converting the intermediate mandelic acid type compound to the aldehyde, and that the end product is produced only in low yield.
In any of these processes, 2,3-methylenedioxybenzaldehyde is formed as a by-product in addition to the end product, and hence there is a problem that separation and purification of the end product from the reaction product is difficult.
In this situation, the inventor has investigated a novel process for preparing aromatic aldehyde derivatives represented by the general formula (IX) as described above and, as a result, has discovered an extremely advantageous process which follows an absolutely different route from the conventional routes, which removes the defects with the conventional processes, which provides the end product in high yield and in high purity, and which involves steps easily put into industrial practice, thus having achieved the present invention.